This invention relates to terpene polymers and more particularly to high molecular weight beta-phellandrene-maleic anhydride copolymers.
Turpentine, turpentine distillation cuts, and acid-isomerized turpentine are economical sources of ten-carbon olefins and di-olefins called terpenes. The electron-rich unsaturation present in terpenes makes them attractive coreactants with electron deficient olefins, e.g. maleic anhydride, in Diels-Alder and Ene reactions. An early exploitation of this chemistry was disclosed by Peterson in U.S. Pat. No. 1,993,031. Peterson reacted turpentine distillates, consisting of alpha-pinene, beta-pinene, dipentene and terpinolene with maleic anhydride at a temperature in the range of about 150.degree. to 200.degree. C. The products of these reactions are referred to as soft resins and are believed to have been 1:1 and 1:2 terpene:maleic anhydride addition products which have molecular weights of 234 g/mol and 322 g/mol, respectively, and will be known hereinafter as "terpene maleic anhydride adducts." These low molecular weight adducts found early utility as components in alkyd resins because of their advantageous solubility behavior, the flexibility they provided in formulating alkyd resins, and their low cost.
Alkyd resins based on terpene maleic anhydride adducts have been incorporated into coating and varnish formulations. However, because the terpene adducts are of low molecular weight and are less reactive toward chain-extending polyols than other alkylidene diacids, the derived coatings have relatively poor film strength, poor heat resistance, and elevated water sensitivity compared to coatings made from other polymers. If a method could be found whereby high molecular weight polymers formed between terpenes and maleic anhydride could be prepared, it is expected that inks, varnishes, paints and coatings based on these polymers would show improved properties.
Attempts to increase the molecular weight of reaction products between terpenes and maleic anhydride are frustrated by the preference of most terpenes to undergo Ene and Diels-Alder reactions with maleic anhydride at elevated temperatures. The tendency of many terpenes to undergo isomerization in the presence of even a trace amount of acid further complicates the reaction chemistry of terpenes and maleic anhydride. Non-conjugated terpenes are frequently seen to isomerize to a conjugated form amenable to Diels-Alder reactions.
In U.S. Pat. No. 4,046,748 and U.S. Pat. No. 4,107,420, Schluenze teaches that the addition of controlled amounts of iodine to a reaction mixture comprising maleic anhydride and non-conjugated monocyclic terpene(s) will increase the ratio of diadducts (two maleic anhydrides react with one terpene) to monoadducts (one maleic anhydride reacts with one terpene). In no case does Schluenze indicate that products with molecular weights higher than that of diadduct (332 g/mol) are formed under any of the reaction conditions disclosed. Apparently, the addition of iodine encourages various Ene and Diels-Alder reactions to occur, but not polymerization.
Other descriptions of terpene maleic anhydride adductions and diadductions, derivatives of the (di)adducts, as well as uses for the (di)adducts and derivatives are disclosed in several patents and publications, including U.S. Pat. No. 3,043,789, U.S. Pat. No.4,055,576 and U.S. Pat. No. 2,230,230.
Polymers incorporating both maleic anhydride and terpenes have been prepared in the presence of reactive comonomers. In U.S. Pat. No. 4,172,861 Li et al. disclose that materials with high softening temperatures can be formed from the mixture comprising styrene-butadiene rubber, styrene, beta-pinene, maleic anhydride, and a free-radical initiator. Li et al. indicate that limonene can be used in place of beta-pinene, but they neither indicate nor claim that useful materials can be formed under their reaction conditions in the absence of styrene and styrene-butadiene rubber.
U.S. Pat. No. 2,383,399 to Lundquist discloses the preparation of terpolymers from a reaction mixture comprising maleic anhydride, terpene(s), and a third comonomer "capable of rapid and exothermic polymerization with maleic anhydride". This third comonomer is preferably styrene. The reaction of styrene, maleic anhydride and dipentene (racemic limonene) proceeds to give terpolymer in 75% yield, while the same reaction run in the absence of styrene leads to an unidentified polymer in a yield of 37%. The reaction of styrene, maleic anhydride and camphene proceeds to give terpolymer in 34% yield, while the same reaction run in the absence of styrene did not form polymer in a quantity sufficient for isolation. It is broadly claimed that all terpenes with the formula C.sub.10 H.sub.16 and having not more than two double bonds per molecule may be used in this terpolymerization. No claim is made for the preparation of copolymers between terpenes and maleic anhydride.
German patent No. 1,694,829 serves as another example of the preparation of terpolymers containing terpenes, maleic anhydride and reactable termonomers. The formation of a polymer in the absence of a reactable termonomer is not indicated.
Little success has heretofore been achieved in the preparation of high molecular weight polymers made solely from terpenes and maleic anhydride. One approach to preparing high molecular weight materials consisting solely of terpene and maleic anhydride has been to prepare a terpene homopolymer by methods well known in the art and in a subsequent operation attach maleic anhydride onto the preformed homopolymer, in some instances in the presence of an organic peroxide. Examples of this general approach can be found in disclosures made in U.S. Pat. No. 3,193,449, U.S. Pat. No. 3,375,130, and U.S. Pat. No. 4,670,504.
Such maleinated terpene homopolymers should be distinguished from the object of this invention, which, as will be described in more detail, is the copolymer formed between a terpene and maleic anhydride wherein both the terpene and maleic anhydride contribute to the backbone of the polymer.
Direct copolymerizations of terpenes with maleic anhydride are almost without precedent. The free-radical induced copolymerization between limonene and maleic anhydride has been studied recently by Doiuchi et al. as described in European Polymer Journal Vol. 17, pp. 961-968, (1981). Although mostly interested in the mechanism of the copolymerization, they reported that their highest yield of copolymer occurred after 72 hours of reaction and was only 13%. A detailed study of the copolymer revealed that it was comprised of limonene and maleic anhydride in the molar ratio of 1:2 and had a number average molecular weight of only 1300. W. J. Bailey, in Contemporary Topics in Polymer Chemistry, M. Shen, Ed., Vol. 3, p. 49, Plenum Press, N.Y. (1979) reports that beta-pinene will undergo an alternating copolymerization with maleic anhydride. Bailey makes no mention of the details and yields of this process and does not describe the formation of copolymers between maleic anhydride and any terpene other than beta-pinene.
Successful copolymerization of a terpene and maleic anhydride in high yield to a resin of high melt point and high molecular weight evidently depends on the careful selection of the terpene isomer. Terpenes with cisoid conjugated double bonds, for example alpha-terpinene, will prefer to undergo rapid Diels-Alder adduction. Those with isolated double bonds may undergo limited copolymerization, as is seen, for example, with limonene, or are inert, as is the case with camphene, or isomerize under the reaction conditions, as occurs with terpinolene.